biochemistry - How crowded is the bacterial cell?

Composition of E. coli (dry weight): 55% protein, 20% RNA, 10% lipid, 15% other

Protein concentration is about 100 mg/ml or 3 mM. From the size of an E. coli cell, 1 nM is about 1 molecule/cell. This is ~1000 molecules/cell for HeLa cells.

Diffusion coefficient for an "average" protein: D ~ 5-15 microns^2/s, or ~10 ms to traverse an E. coli. For reference, a small metabolite in water diffuses about 30-100x faster.

Reference: Cell 141:1262, Key Numbers in Biology